Mitochondria are essential for ATP production, calcium homeostasis, and programmed cell death, and mitochondrial dysfunction is a hallmark of neuronal injury and degeneration. Mitochondria are highly dynamic organelles shaped by frequent fission and fusions events. While mutations in broadly expressed mitochondrial fusion enzymes are known to cause common neurodegenerative diseases (Charcot-Marie-Tooth disease and dominant optic atrophy), physiological regulatory mechanisms impacting the mitochondrial fission/fusion equilibrium are poorly defined. We previously identified an outer mitochondrial protein kinase and phosphatase pair, PKA/AKAP1 and PP2A/Bbeta2, which regulate mitochondrial shape via reversible phosphorylation of a highly conserved, inhibitory phosphorylation site (S656) in the mitochondrial fission enzyme dynamin-related protein 1 (Drp1). In addition to controlling neuronal survival, PKA/PP2A-mediated phospho-regulation of Drp1 has profound consequences for dendrite and synapse development in cultured hippocampal neurons. This proposal builds on these in vitro results by exploring the role of PP2A/Bbeta2 and its antagonist PKA/AKAP1 in postnatal brain development and function in vivo. It addresses the overarching hypothesis that OMM- localized PKA and PP2A bidirectionally regulate synaptic connectivity and plasticity and ultimately cognition via Drp1 phosphorylation and mitochondrial dynamics. To this end, aim 1 will analyze brains of AKAP1 and Bbeta2 KO, as well as AKAP1/Bbeta2 double KO mice for altered development of dendrites, dendritic spines, and synapses. Aim 2 examines the impact of these structural changes on synaptic plasticity and learning and memory. Aim 2 also addresses the mechanism by which Bbeta2 and AKAP1 influence postnatal brain development and function by rescuing deficits with wild-type and mutant B?2 and AKAP1 expression, and by replacing endogenous with phospho-mutant Drp1 via stereotaxic delivery of lentivirus. These studies are meant to elucidate regulatory mechanisms controlling neuronal wiring and plasticity via mitochondrial dynamics. Knowledge gained with this proposal may spur the development of better treatments for CNS disorders involving abnormal synaptic connectivity and transmission.